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1. Multiple breeding (raising more than one batch of young per breeding season) is a common life-history tactic that has received very little attention. A simple static optimization model was developed, applicable to iteroparous animals with parental care, that predicts: (1) when an animal should be a multiple breeder, (2) the optimal interval between successive clutches, and (3) when a clutch should be deserted. 2. More specifically, it was predicted that (I) animals should invest less in a clutch when it is followed by another clutch in the same season, and (II) as a consequence the contribution of the first clutch to the parents' fitness will be reduced. 3. These predictions were tested experimentally in a population of Great Tits (Parus M. major L.). The experiment consisted of the removal of second clutches. When second clutches were removed, parents tended their first brood fledglings for a longer period than undisturbed control pairs, in agreement with the first prediction. Removal of second clutches did not affect fledgling survival, but recruits enjoyed higher reproductive success in their first year of breeding when the second clutch of their parents had been removed, in agreement with the second prediction. 4. It is concluded that a trade-off exists between successive reproductive attempts, which will affect the optimal rate of reproductive attempts. [KEYWORDS: life history; multiple breeding; parental care; Parus major; trade-off Parental care; clutch overlap; brood division; parus-major; size; investment; cooperation; postpartum; survival; behavior]